Chapter 20 Heat Sterilization of Wood
appropriate time–temperature schedules assuming the low-
est initial wood moisture content from one of the following
publications:
a) FPL–GTR–130, Heating times for round and rectangu-
lar cross sections of wood in steam (Simpson 2001);
b) FPL–RP–607, Heat sterilization time of ponderosa pine
and Douglas-fir boards and square timbers (Simpson
and others 2003);
c) FPL–RP–604, Effect of wet-bulb depression on heat
sterilization time of slash pine lumber (Simpson 2002);
or
d) CFIA PI–07, The technical heat treatment guidelines
and operating conditions manual, Option C (CFIA
2006).
Quality Mark
ISPM 15 requires that treated packaging must be marked
with an official stamp that includes an International Plant
Protection Convention (IPPC) symbol, an International
Standards Organization (ISO) two-letter country code, and
abbreviation of the type of treatment used (heat treatment is
indicated by the mark HT), and a unique number assigned
by the country’s national plant protection organization to the
producer of the wood packaging material, who is responsi-
ble for ensuring that appropriate wood is used and properly
marked (Figure 20–5). If wood packaging materials arrive in
a member country without this quality mark, officials at the
port of arrival have the right to refuse entry or require treat-
ment (such as fumigation) at the port—a costly situation.
Recycled, remanufactured, or repaired wood packing mate-
rial should be recertified and remarked. All components of
such material are required to be properly treated.Other Considerations
Heating capacity—It is critical in heat sterilization that the
heating and humidification system be designed to meet the
production schedule. Typically, the heating capacity of aTable 20–8. Summary of heating times (at 160 °F (71 °C)) to 133 °F (56 °C)) for
ponderosa pine square timbers estimated by multiple regression modelsa
Wet-bulb
depression
(°F)Initial
temperature
(°F)Heating time (min)b
4 by 4 6 by 6 8 by 8 10 by 10 12 by 12
2 40 155 (225) 29 7 (429) 473 (682) 677 (980) 9 0 (1,321)
4 40 178 (259) 343 (492) 545 (782) 780 (1,123) 1,0 4 (1,512)
6 40 194 (282) 37 2 (535) 592 (850) 848 (1,220) 1,13 (1,643)
8 40 206 (299) 395 (569) 628 (903) 899 (1,296) 1,2 0 (1,745)
10 40 215 (314) 413 (597) 657 (947) 941 (1,359) 1,2 6 (1,830)
12 40 223 (327) 42 9 (621) 682 (986) 977 (1,414) 1,31 (1,904)
2 50 138 (200) 265 (382) 421 (609) 603 (878) 8 0 (1,185)
4 50 159 (229) 305 (437) 485 (697) 695 (1,003) 93 (1,354)
6 50 173 (249) 33 2 (475) 527 (756) 755 (1,088) 1,01 (1,468)
8 50 183 (264) 35 2 (504) 559 (802) 801 (1,155) 1,0 7 (1,558)
10 50 192 (277) 368 (529) 585 (841) 838 (1,210) 1,1 2 (1,633)
12 50 199 (288) 38 2 (550) 607 (875) 870 (1,258) 1,1 6 (1,697)
2 60 125 (182) 241 (350) 383 (559) 548 (807) 73 (1,091)
4 60 144 (208) 278 (400) 441 (638) 632 (921) 8 4 (1,245)
6 60 157 (226) 30 2 (433) 479 (692) 687 (998) 9 2 (1,349)
8 60 166 (240) 32 0 (460) 508 (734) 728 (1,058) 9 7 (1,430)
10 60 174 (251) 335 (482) 532 (769) 762 (1,108) 1,0 2 (1,497)
12 60 181 (261) 348 (501) 552 (799) 791 (1,151) 1,0 6 (1,555)
2 70 116 (169) 22 2 (326) 353 (523) 506 (755) 6 7 (1,022)
4 70 133 (193) 25 6 (372) 407 (596) 583 (860) 78 (1,164)
6 70 145 (210) 278 (403) 442 (645) 634 (932) 85 (1,260)
8 70 154 (222) 295 (427) 469 (684) 672 (987) 9 0 (1,335)
10 70 161 (233) 30 9 (448) 491 (716) 703 (1,033) 9 4 (1,398)
12 70 167 (242) 321 (465) 510 (743) 730 (1,073) 9 7 (1,451)
2 80 108 (160) 20 7 (308) 330 (494) 472 (715) 63 (968)
4 80 124 (182) 23 9 (351) 380 (563) 544 (814) 73 (1,102)
6 80 135 (197) 26 0 (380) 413 (609) 591 (880) 7 9 (1,192)
8 80 143 (209) 275 (403) 438 (645) 627 (932) 8 4 (1,262)
10 80 150 (219) 288 (421) 458 (675) 656 (975) 88 (1,321)
12 80 156 (227) 29 9 (438) 476 (701) 681 (1,013) 91 (1,371)
aT°C = (T°F – 32)/1.8; °C = °F/1.8; 1 in. = 25.4 mm.
bValues in parentheses are 99% upper confidence bounds of heating times.